Temperature dependence of the anisotropic magnetic penetration depth and lower critical field of single-crystal Pb2Sr2(Y,Ca)Cu3O8+ delta.

Abstract

The temperature dependence of the penetration depth of single-crystal ${\mathrm{Pb}}_{2}$${\mathrm{Sr}}_{2}$(Y,Ca)${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ has been determined in the vicinity of ${\mathit{T}}_{\mathit{c}}$ (\ensuremath{\sim}75 K) using intermediate-field reversible-magnetization measurements. The ab-plane penetration depth in the restricted region near ${\mathit{T}}_{\mathit{c}}$ was found to follow clean-limit BCS behavior from which an estimate of 2575 \AA{} for ${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$(0) was obtained. The effective-mass anisotropy parameter, \ensuremath{\gamma}=(${\mathit{m}}_{\mathit{c}}$/${\mathit{m}}_{\mathit{a}\mathit{b}}$${)}^{1/2}$, was found to be 2.5, which together with the former result yields a value of 6425 \AA{} for ${\ensuremath{\lambda}}_{\mathit{c}}$(0). In addition, the temperature dependence of the anisotropic lower critical field was determined from observations of the onset of deviation from perfect diamagnetism. The estimates obtained for the zero-temperature lower critical field, ${\mathit{H}}_{\mathit{c}1}$(0), were 95\ifmmode\pm\else\textpm\fi{}10 G for H\ensuremath{\perp}c and 505\ifmmode\pm\else\textpm\fi{}20 G for H\ensuremath{\parallel}c.